The invention refers to a control device for overhead conveyors equipped with at least two actuators, specifically crane and crane trolley drive units.
For instance, a control device with a hanging control panel for crane and crane trolley drive units of cranes with traversing crane trolleys is known from EP 0 592 795 A1, in which a hanging control panel suspended from a crane is used to control the movement of hoisting gear located on a crane trolley above the operator. The hanging control panel is used to control the up-and-down movement of the hoisting gear. It controls the crane's drive unit and the crane trolley's drive unit simultaneously. For this reason, the hanging control panel is connected to corresponding controls via a control line. The hanging control panel emits control signals, which are transmitted to the control. Aside from control signals, the hanging control panel also generates safety signals, which are initiated manually, for instance an emergency stop of the hoisting gear initiated by the operator. The transmission of control and safety signals occurs via signal lines (conductor or contact lines) running parallel in the form of switch states dependent on certain levels or coded continuously variable signals (PWM code), while at least one line is used for each control and safety signal.
It is further known to transmit control and safety signals via a data bus when conductor lines are used with overhead conveyors with a high number of special functions. A central control is used to control the drives via control signals transmitted by a data bus. Safety signals are transmitted via separate conductor lines independently from control signals as switch states dependent on certain levels.
These known control devices have the disadvantage that they are relatively expensive and that impacts and collisions may occur nonetheless, especially if a hanging control panel, and therefore its emergency stop function, fails.
The purpose of the present invention is to specify a simple control device for overhead conveyors and ensure a conveyor's increased operational safety.